Heat exchanger

ABSTRACT

The invention relates to a heat exchanger.  
     This exchanger is of the type which has at least one route for flow of a cooling fluid, such as water, a cooling agent or even air, and at least a second route for flow of a fluid such as air. At least the second route has a number of flow channels. The exchanger is characterized by the fact that it has some means of evacuation of the water which condenses on the walls of the air flow channels by suction.  
     The invention can be used in heat exchangers.

[0001] The invention relates to a type of heat exchanger that has twofluid flow routes, which in particular are crossed or parallel. A firstroute having a number of flow channels for a first cooling fluid, suchas water, and the second route having a number of flow channels for agaseous fluid such as air.

[0002] In the known heat exchangers of this type, the air which flowsthrough the channels of the second route is cooled by the water to atemperature close to that of the water. Consequently, a part of themoisture contained in the air flow condenses on the walls of thechannels. For thermal reasons, the channels can be narrow in at leastone of their dimensions, and capillary forces can therefore exertthemselves on the condensate which then accumulates on the walls of thechannels. The first consequence is that large quantities of condensatecan be carried along by the air flow in the case of an increase of airflow rate. This phenomenon, called the “wave” phenomenon, isunacceptable for certain applications. Two other consequences of thisaccumulation are an increase of the load loss of the exchanger in thiscircuit and a decrease of the heat exchange because of the thickness ofthe condensate retained on the fins.

[0003] The objective of the invention is to propose a heat exchangerwhich minimizes the just stated disadvantage of the known heatexchangers.

[0004] In order to accomplish this purpose, the heat exchanger accordingto the invention is characterized by the fact that it has some means ofevacuation of the condensed water by suction at the outlets of the airflow channels.

[0005] According to a characteristic of the invention, the wateraccumulated at the ends of the channels is drawn through holes whichjoin with a space in which a low pressure predominates.

[0006] The invention will be better understood and other aims,characteristics, details and advantages of it will be more clearly shownin the following explanatory description given in reference to theappended schematic drawings which are given only as examples,illustrating an embodiment of the invention and in which:

[0007]FIG. 1 is a schematic perspective view of a heat exchangeraccording to the present invention;

[0008]FIGS. 2 and 3 are perspective views, with part torn away, of twoother embodiments of the heat exchanger according to FIG. 1, and

[0009]FIGS. 4a, d, c, d are views in the direction of arrow of FIG. 1and show four configuration possibilities of water suction holes of theheat exchanger according to the invention.

[0010] As shown in the figures, a heat exchanger according to thepresent invention includes, superposed in an alternating and crossedmanner, route 2 for the flow of a cooling fluid, such as water, androute 3 for the flow of a gaseous fluid such as air. Routes 2 and 3 aredelimited between two walls 5 in the form of plates, which are paralleland rectangular. These routes are closed by lateral wall elements 7 ontwo opposite sides, and they are open on the other two parallel sides.The delimited space is subdivided into a number of flow channels 8 byparallel separation fins 9. In the example represented in the figures,the fins are part of an insert made up of a sheet configured so as tohave a zigzag profile. The insert can have any shape in the direction ofthe flow.

[0011] As seen in FIG. 1, in a heat exchanger according to theinvention, the walls in plate form 5 extend a predetermined distancebeyond ends 11 of the air flow channels, which are the ends of theinsert delimiting these channels. This part of the plates is thereforefree of fins. FIG. 1 also shows that in water flow route 2, space 15between two spaces 14 is also free of fins 9. This space 15, delimitedlaterally by end wall 7 and by exterior fin 9 formed by the end limb ofthe insert or another end wall, is connected in a manner not shown toa[nother] space, also not shown, in which a low pressure predominates.

[0012] An essential characteristic of the invention lies in the factthat walls 5 have, in their fin-free part 14 near ends 11 of the airflow channels, through-holes 17 which then emerge in space 15 in which alow pressure predominates. These holes 17 are intended to permit thesuction of the water condensed on the walls of the fins and the arrival[of the condensate] in the channels at ends 11 under the effect of theflow of water. This water is therefore evacuated by suctionthrough-holes 17. These holes 17 stop the accumulation of the condensateat ends 11 and thus the release of this water in the form of“spontaneous waves”. The holes 17 are located a relatively shortdistance from the ends.

[0013]FIGS. 2 and 3 show two particularly advantageous configurations ofthe ends of fins 9. The objective of these configurations is to modifythe geometry of the exchanger and to create pressure gradients in orderto overcome the capillary forces which tend to retain the water on thefins. In the version represented in FIG. 2, the ends are curved or bowedin such a way that the median part of each fin is recessed, and thecondensate is pushed by the air flowing in the channel towards thefin-free plate part 14 and thus in the direction of suction holes 17. Inthe version according to FIG. 3, each fin end 11 is cut out at the topand at the bottom on 19 along an L-shaped line so that the median parthas the shape of a U whose base 20 projects in the direction of the flowof the air. Suction holes 17 are made in plate parts 14 in the L-shapedcut-out zone.

[0014] This second variant amounts to putting holes 17 at the end of theair channels. It is also possible, however, to consider putting holes 17farther upstream in the air channels in a line or distributed in such away as to optimize the suction taking place, either in a separate spacefrom the cooling channels or directly in the channels of the coolingfluid.

[0015] As an example, FIG. 1 shows at 27, holes which emerge in acooling fluid channel. Of course, one could provide several lines ofholes emerging in cooling channels, which differ and are offset in thedirection of flow of the air. Thus, the invention provides suctionopenings at the site of the flow channel outlets 17 or suction openingsemerging either in a cooling fluid channel as at 27 or in a slight lowpressure space 15.

[0016]FIGS. 4a to 4 d illustrate several embodiments of suction holes 17to 27. In FIG. 4a, holes 17 are in the form of circular holes 22. InFIG. 4b, each hole has the shape of a roughly rectangular slit 23. Threeslits are aligned over the width of suction part 14. In the versionrepresented in FIG. 4c, hole 17 has the shape of an S-shaped slit 24.Over the width of suction part 14, three slits 24 are aligned andarranged in such a way that their ends overlap in height. One thusobtains a suction effect over the whole width without interruption whileavoiding mechanical weakening of the resistance of the wall.

[0017] The hole version according to FIG. 4d has the particularcharacteristic that two parallel rows of holes are made in suction part14. The two series of holes are offset in such a way that a hole of onerow is between two holes of the other row. These holes can of coursehave any suitable shape which can differ in the two rows. Thus, in FIG.4d, one row has circular holes 25, and one row has triangular holes 26.

[0018] Generally, the shapes of the ends of the fins and the shapes ofthe holes, which are represented in the figures, are only given asexamples and can be modified provided that the suction of the water isensured on the wall of the channels all along these channels and/orwhich would accumulate without evacuation through the holes at the endsof the fins. Of course, the cooling fluid could be of any other suitablenature and could be a cooling agent, any liquid other than water or evenair.

1. A heat exchanger of the type which has at least one route for flow ofa cooling fluid, such as water, a cooling agent or even air, and atleast a second route for flow of a fluid such as air, at least thesecond route having a number of flow channels, characterized by the factthat it has some means of evacuation by suction of the water whichcondensed on the walls of the air flow channels.
 2. A heat exchangeraccording to claim 1, characterized by the fact that the means ofevacuation have suction openings (17) which join with the channels forflow of the cooling fluid.
 3. A heat exchanger according to claim 1,characterized by the fact that the means of suction are provided atoutlets (11) of gaseous fluid flow channels (8).
 4. A heat exchangeraccording to claim 3, characterized by the fact that the means ofevacuation of the water have suction openings (17) provided at the siteof outlets (11) of air flow channels (8).
 5. A heat exchanger accordingto claim 4, characterized by the fact that suction openings (17) joinwith space (15) in which a low pressure predominates.
 6. A heatexchanger according to one of claims 1 to 5, in which air flow channels(8) are juxtaposed and formed between two roughly parallel plates (5),characterized by the fact that these plates (5) extend at (14) beyondends (11) of air flow channels (8) and by the fact that suction openings(17) are formed by through-holes which join with said low pressure space(15).
 7. A heat exchanger according to claim 6, characterized by thefact that the aforementioned space (15) is delimited in cooling waterflow route (2) and by the fact that suction holes (17) emerge in thisspace (15).
 8. A heat exchanger according to either of claims 6 and 7,characterized by the fact that ends (11) of walls (9) delimiting airflow channels (8) between two plates (5) have a shape which ensuresrouting of the condensate towards suction openings (17).
 9. A heatexchanger according to one of claims 6 to 8, characterized by the factthat ends (11) of delimiting walls (9) of flow channels (8) between twoplates (5) have a curved shape so that the end is recessed in its medianpart.
 10. A heat exchanger according to one of claims 6 to 8,characterized by the fact that end (11) of delimiting wall (9) of theair flow channels between two plates (5) is configured so that themedian part projects in the direction of the flow of the air withrespect to the parts adjacent to plates (5) and by the fact that suctionopenings (17) are provided roughly under the projecting parts.
 11. Aheat exchanger according to one of claims 6 to 10, characterized by thefact that suction holes (17) are formed by at least one series of holes(22) distributed over the width of projecting part (14) of plates (5).12. A heat exchanger according to one of claims 6 to 10, characterizedby the fact that suction holes (17) are formed by at least one row ofslits (23) aligned over the width of part (14) of plates (5).
 13. A heatexchanger according to claim 12, characterized by the fact that slit(23) has the shape of an S (24) and by the fact that the slits arealigned so that their ends overlap in height.
 14. A heat exchangeraccording to claim 11, characterized by the fact that it has at leasttwo rows of holes (25, 26), of different shape if necessary, a hole ofone row being in the middle of a hole two holes of another row.